Such arrangements have been described in patent document EP-B-O 030 210. Such arrangements incorporated into an apparatus for the observation of an eye in view of subsequent treatment by laser surgery permit not only to visualize the power beam which is itself invisible but also to check that no obstacle (such as the iris, for instance), is found in the path of said beam.
This prior art will now be briefly reviewed. For this purpose FIG. 1 herein will be referred to.
The apparatus includes a first light source 230 which emits a power beam 23 intended for surgical treatment. This beam is emitted along a first optical axis 1 from for instance a solid state laser source operating in a pulsed mode (for example in the so-called Q switching mode). The cross-section of the beam may be modified either by means of a diaphragm with an iris 131 or by optical adaptation means here symbolized by block 24. At the output of these elements the beam propagating along axis 1 exhibits a predetermined cross-section. This section here is cylindrical having a diameter D.sub.1. However, in a known manner, it could also be for instance square or rectangular.
The apparatus further includes a second light source 28 which emits a visible light beam 29 of low power. This beam is emitted along a second optical axis from for instance a He-Ne laser. The beam 29 is received by an arrangement including a rotatable element 33 turning for instance in the sense of arrow A, around the second optical axis 2. This element includes in the cited document, a set of prisms and mirrors transforming the beam 29 into two elementary parallel beams 30 and 31. When the element 33 rotates the elementary beams generate a luminous tubular beam 32 having a diameter D.sub.2 and co-axial with the second optical axis 2. The rotatable element is arranged in a manner such that the diameter D.sub.2 of the tubular beam 32 is equal to the diameter D.sub.1 of the power beam 34. This adaptation is brought about in the cited document by a sliding lever controlling two prisms. From each of these prisms is emitted an elementary beam, said beams being adapted to be spread apart or brought together through manipulation of the lever.
FIG. 1 further shows that the apparatus is provided with two half-reflecting mirrors 9 and 27 which have as purpose to combine the power beam 34 and the luminous tubular beam 32 along a third optical axis 3 in a manner such that beam 32 surrounds beam 34.
In the path of the third optical axis 3 is arranged a lens 41 which may be axially displaced by means of a mechanism 400 which serves to adjust the focal point of the lens onto the place to be treated or to be observed.
Thus, at the output of lens 41 is found a light cone the vertex angle of which is predetermined on the one hand by the focal length of the lens and on the other hand by diameters D.sub.1 and D.sub.2 of beam 34 and beam 32 respectively. The cone of the beam 34 is then surrounded by an envelope cone issuing from beam 32.
The focal point of lens 41 may be observed by a practitioner 5. The eye of the practitioner bears on an optical complex 6 which defines an observation beam 4 finally being superposed onto the optical axis 3. This complex may also be a binocular type system.
The luminous output cone of lens 41 is deviated by a contact lens 11 which the practitioner supports on the eye 7 of the patient in a manner such that the focal point 12 of said lens falls at the desired location.
The reader may refer to the cited document in order to obtain still further details concerning the operation of the entire system. One may recall here simply that the observation beam is provided with a large depth of field and that consequently the visual observation is insufficient to locate with precision the position of the focal point of lens 41 which explains the presence of the second light source 28 so as to enable an extremely precise positioning of the focal point of the power beam 34. It will be noted in passing that this second source may be coherent or non-coherent.
As has been mentioned hereinabove, the rotating element 33 includes a set of prisms and mirrors. In practice, the manufacture, assembly and regulation of such elements is extremely expensive. Furthermore, such equipment is heavy and voluminous which increases the weight and space occupied by the arrangement.